This invention relates generally to combustors and, more particularly, to gas turbine combustors.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Aircraft are governed by both Environmental Protection Agency (EPA) and International Civil Aviation Organization (ICAO) standards. These standards regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO) from aircraft in the vicinity of airports, where they contribute to urban photochemical smog problems. In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC and CO).
At least some known gas turbine combustors include between 10 and 30 mixer assemblies, which mix high velocity air with a fine fuel spray. These mixer assemblies usually consist of a fuel nozzle located at a center of a swirler for swirling the incoming air to enhance flame stabilization and mixing. Both the fuel nozzle and the mixer assembly are located on a combustor dome. In conventional gas turbine combustion systems, the fuel nozzles are inserted into the dome assembly in an axial orientation. This approach leads to several drawbacks that must be dealt with during a combustor design phase. Axial configured fuel nozzles require an open volume upstream from the dome face to allow for the insertion and extraction of the fuel nozzle without removing the combustor. This additional volume or envelope adds extra length, cost and/or weight to the engine, without adding any benefit to the operation of the engine. Additionally, a long fuel nozzle stem is needed to connect the fuel nozzle tip to a flange of the dome assembly, which also adds cost and/or weight to the engine, and adversely affects the natural frequency of the fuel nozzle and/or the heat transfer within the fuel nozzle.